Micro-grid Layered Protection Based On LabVIEW

Micro-grid protection is an important issue on micro-grid research. There is a big difference between the micro-grid power system protection and traditional power system protection. In order to achieve the micro-grid protection, my paper will firstly analyze the protective properties of micro-grid, including the different effects of distributed power, grounding methods and operating methods. Then the paper comes to the micro-grid layered protection according to the above analysis, it will classify the load into different quality grade on the basis of the importance and will use LabVIEW PC software to design micro-grid layered protection program.For the hardware parts, this paper is mainly design a hardware circuit which is required to protect the micro-grid and also built a hardware platform. The hardware platform includes IPC, Advantech IPC PCI card, signal conditioning circuit, steering circuit for controlling contactor and the signal back circuit for contactor status transmission. To monitor and protect grid-connection, inverters, energy storage unit and the load of power quality in real time visually, I will use IPC as PC, LabVIEW as PC software, combining with PCI boards to establish a micro-grid layered protection system based on LabVIEW.For the software parts, this paper builds a micro-grid topology by LabVIEW software and also rewrites micro-grid power quality monitoring and layered protection program. Topology includes the switches that can control all the micro-grid devices to achieve real-time monitoring of the power of every part inside micro-grid, so as to monitoring micro-grid in real-time status on this interface. Power quality analysis part shows inside and outside the network voltage and current waveforms of PCC, also the current waveforms of load and inverter. It is feasible by selecting to monitor current harmonic distortion to monitor the balance of the PCC voltage and to write down the basic information recording electrical parameters. Protection parts include overcurrent protection, anti-current protection, over voltage and low frequency cut machine frequency load shedding. When the value is greater than the protection threshold monitoring, protection functions start to realize the micro-grid protection.Finally, it is obvious that the correctness and feasibility of the designed micro-grid system via layered protection can be proved by experiments on the micro-grid experimental platform. Micro-grid topology interface can control microcomputer network contacts corresponding to all the devices on-off and can display inverter and load power conditions normally. Power Quality Analysis interface can calculate the voltage balance of grid-connection correctly and analyze the harmonic content in chart, so as to show voltage waveform of the grid-connection and the operating current waveform of all inverters in real-time and to record voltage, current, the basic parameters. On micro-grid layered protection interface, we can not only be able to select the desired function is protected by controlling the switch protection function, but also can customize the protection module in accordance with the operator’s need to design other additional protection. In addition, failure information will be recorded in the file set folder when three-phase is unbalanced or harmonics is over-criterion.